1. Technical Field
This present invention relates to a temperature detecting circuit and method, more specifically, to a temperature detecting circuit and method with less hardware requirement and capable of detecting current and temperature at the same time.
2. Description of Related Art
Please refer to U.S. Pat. No. 6,870,352. A current sensor (30) is shunt to an inductor (18) to detect the inductor current. The current sensor is also adopted as a compensation circuit to compensate the temperature coefficient of the inductor (18). Hence, the temperature coefficient of the signal representing the inductor current generated by the current sensor (30) is zero. Therefore, when accurate output current detection is required for reference on control in a voltage converter circuit, the current sensor (30) can be applied to alleviate the influence of temperature. For example, the current sensor (30) can be applied in a voltage converter circuit with the feature of adaptive voltage positioning (AVP), which renders the output voltage on the output node of the voltage converter circuit decreasing with the increase of the output current in order to allow larger tolerance range in a transient response of the output voltage. As a result, the decoupling capacitors on the output node can be reduced, which saves hardware cost and size, and power consumption can also be saved a bit under the criteria of complying with the specification of output voltage range.
Please refer to U.S. Pat. No. 6,998,827. A detecting device (2) is adopted to detect the output current of a voltage converter circuit and generate a detected current Ifb which is proportional to the output current and flows through a resistor Rfb coupled between an inverting terminal of an amplifier (3) and an output terminal of the voltage converter circuit. When the output current increases, the voltage drop between the inverting terminal of the amplifier (3) and the output terminal also increases, and the function of AVP is thus realized. However, in this prior art, since the Ifb and Rfb have their own temperature coefficient, the output voltage will change with temperature. In order to overcome this issue, Rfb is replaced by a compensation circuit to compensate the temperature coefficient of Ifb and the temperature coefficient of the output voltage is essential zero.
However, in the design of the voltage converter circuit, it is a usual technique to detect change on temperature for realizing over-temperature protection (OTP) or other temperature-related compensations. In the above-mentioned prior arts, the problem is solved by directly compensating the temperature coefficient of the detected signal of the output current. Nonetheless, these prior art cannot be adopted in other purposes relating to temperature, and extra circuit will be needed. For example, when OTP function is required in a voltage converter circuit, a circuit disclosed in FIG. 1 will be additionally required. In FIG. 1, a negative temperature coefficient (NTC) resistor and a normal resistor are adopted as a voltage divider, which generates a voltage ratio compared with a reference voltage Vfref. When the temperature is higher than a default value, the output of the comparator change the signal state thereon to inform the voltage converter circuit shut-down to prevent from mal-function of the circuit or even unsafety issue such as burning. However the NTC resistor, which is also inevitably adopted in the above-mentioned prior art, is a special device. Hence, if the NTC resistor can be shared in the designs of different purposes, the hardware cost and size can be further saved.